Transmodulation of epidermal growth factor binding by platelet-derived growth factor and 12-O-tetradecanoylphorbol-13-acetate is not sodium-dependent in Balb/c/3T3 cells.
The addition of platelet-derived growth factor (PDGF) to many types of cells causes a rapid decrease in high affinity binding of 125I-epidermal growth factor (EGF), a process which has been termed transmodulation. Treatment with the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) also results in the transmodulation of the EGF receptor in many cell types. PDGF can transmodulate EGF binding through a mechanism that is not dependent on protein kinase C activity. A recent report (Wattenberg, E. V., McNeil, P. L., Fujiki, H., and Rosner, M. R. (1989) J. Biol. Chem. 264, 213-219) described the requirement for a sodium ion influx in the down-modulation of the EGF receptor stimulated by a non-TPA-type tumor promoter, palytoxin, in Swiss 3T3 cells. We tested for a similar sodium requirement in Balb/c/3T3 and Swiss 3T3 cells stimulated by PDGF or TPA in Balb cells treated with TPA for prolonged periods to down-regulate protein kinase C activity. Our results clearly show that the PDGF- and TPA-stimulated transmodulation of the EGF receptor does not require external sodium nor is the process affected by amiloride. In each of these experiments, the loss of 125I-EGF binding occurred to a similar extent and at a similar rate in the presence or absence of sodium. Intracellular pH also did not appear to have a role in the response. The sodium ionophore, monensin, was previously shown to bring about the down-modulation of 125I-EGF binding in Swiss cells. However, our results indicate that monensin-induced transmodulation of the EGF receptor occurs with or without external sodium, suggesting that the loss of binding is not the result of a sodium ion influx. These findings demonstrate that an increase in intracellular sodium does not cause nor is it required for PDGF- or TPA-stimulated EGF receptor transmodulation.
Olson
J E
JE
Department of cell Biology, Vanderbilt University, Nashville, Tennessee 37232.
Pledger
W J
WJ
D000818:Animals; D002478:Cells, Cultured; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008985:Monensin / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D010982:Platelet-Derived Growth Factor; D011994:Recombinant Proteins; D004815:Epidermal Growth Factor; D008985:Monensin; D012964:Sodium; D066246:ErbB Receptors; D013755:Tetradecanoylphorbol Acetate